understand the three energy systems, imagine hiking up a steep grade. Suppose that you want to race your friends up it, so you begin to sprint. You feel fresh and have tons of energy. The energy you get for the first 8 to 12 seconds comes from the ATP-PCr system, which is anaerobic (without oxygen). It is the fastest available system you have. PCr is phosphocreatine, and when this bond is broken down by creatine kinase, the energy released is used to regenerate ATP.
Now you are moving fast on the steep terrain, but you slow down a little because your muscles start to burn. This burning means that your body is trying to find other sources of energy. This is when the glycolytic pathway takes over. This pathway actually kicked in at the same time as the ATP-PCr system did, but it takes a bit of time and is much slower to regenerate ATP. The glycolytic pathway uses glycogen stored in the muscles, takes glucose from the blood, and uses glycerol from triglycerides to regenerate ATP and keep you moving uphill. For ATP to be regenerated, 10 chemical reactions must take place. As a result, by-products are created: pyruvate and NAD+. At this point, if you keep climbing, there are two possibilities for regenerating more ATP.
KEY TERMS FOR ENERGY PRODUCTION
There’s no need to memorize these terms, but use this list to better understand the processes of energy production in the body.
Acetyl-CoA: A very important molecule that is involved in all reactions of energy production, such as the Krebs cycle.
Adenosine diphosphate (ADP): In order for ATP to provide energy for any given reaction, it has to split away one phosphate to release this energy, forming adenosine diphosphate (ADP). ATP can then be reformed when a free phosphate group is attached by spare energy and is stored again when it’s time to release a phosphate for another reaction. This recycling can occur indefinitely.
Adenosine triphosphate (ATP): This is the energy currency in all living cells. In humans it drives muscle contractions, nerve impulses, and just about any other reaction.
ATP-PCr system: This energy system provides immediate energy. Energy is released quickly and lasts up to 12 seconds in high-power movements such as bouldering or the beginning of any activity.
Beta-oxidation: The breakdown of fatty acids for energy use. We rely on this system to provide consistent energy during most endurance activities.
Creatine kinase: A critical enzyme used during the breakdown of phosphocreatine, splitting the phosphate group and using the energy released from this reaction to attach this phosphate to ADP for energy storage. This reaction is also reversible.
Electron transport chain: Found inside the mitochondria and used in tandem with the Krebs cycle, it is a “system” of rapidly moving electrons that creates kinetic energy that helps to regenerate ATP.
Gluconeogenesis: The formation of glucose from noncarbohydrate sources such as fats and proteins.
Glycogen: Units of glucose stored in body tissue.
Glycogenesis: The formation of glycogen from glucose.
Glycogenolysis: The breakdown of glycogen to glucose.
Glycolysis: The energy system that breaks down glucose to pyruvate that is eventually used to regenerate ATP.
Glycolytic pathway: Interchangeable term used for glycolysis.
Krebs cycle: One of two systems in the mitochondria that produces ATP during oxidative phosphorylation.
Mitochondria: Organelles found in cells that act as power factories, producing large amounts of ATP.
NAD+ and NADH: These are electron donors and acceptors. They are used to help move electrons through the electron transport chain to produce energy.
Oxaloacetate: A by-product of carbohydrate metabolism that can also be formed by gluconeogenesis. It’s an important intermediate for the Krebs cycle to produce ATP.
Oxidative phosphorylation: The aerobic energy system that produces the most ATP for endurance activities.
Phosphate (P): A substance used for energy in cells.
Phosphocreatines (PCr): A creatine molecule with phosphate groups attached to it that provides energy to form ATP.
Pyruvate: A molecule formed from the process of glycolysis and a key molecule that starts the process of the Krebs cycle. It can also be converted to lactate.
Triglycerides: An important energy source stored in fat cells formed from fatty acids. These can be released to use when energy is needed.
Research has shown that supplementation of creatine can help increase the availability of PCr, improve the amount of force your muscles produce, and improve power endurance, which is so important for difficult climbing objectives.
Possibility #1: Fast Glycolysis (Anaerobic)
If you continue at the same intensity for the next 10 to 80 seconds, and you have limited oxygen in the system (that is, if you are gasping for air), energy production will follow the path of anaerobic or fast glycolysis (burning glucose). This process will result in a surplus of hydrogen ions. The problem with hydrogen ions is that they fatigue muscle cells and build up as acid (metabolic acidosis). However, to put it simply, a buffer is created so that muscle contraction can continue. This buffer, called lactate, is formed from a pyruvate and NAD+ attaching to the hydrogen ions, decreasing the acidity. Each time you gasp for air, providing oxygen, this connection breaks and leaves a pyruvate available again to pick up another hydrogen ion. As long as you continue to have just enough oxygen in the system to match the intensity, your system will continue to generate ATP. This cycle persists until you take a break or the intensity becomes too much for the system.
RECIPES TO AVOID METABOLIC ACIDOSIS
•Potato Chestnut Gnocchi with Arugula Pesto
•Banana Coconut Virgin Daiquiri
•Chocolate Banana Jerky
It is a common misconception that lactate or “lactic acid” is what causes delayed-onset muscle soreness (DOMS), or the feeling of fatigue or burning in the muscles. During exercise, lactate takes up excess hydrogen, which helps you continue to exercise. Metabolic acidosis is actually the cause of the burning sensation in the muscles during high-intensity work and is a sign of fatigue, often forcing you to slow down. This acidosis happens outside the mitochondria when too many hydrogen protons accumulate from ATP hydrolysis (the combination of ATP and water). Some supplements that may help clear metabolic acidosis are cordyceps mushrooms, creatine, and beta-alanine (for more information on supplementation, see chapter 12). Foods that help prevent acidosis because of their bicarbonate-and potassium-rich content are bananas, leafy greens, tomatoes, and potatoes.
Possibility #2: Oxidative Phosphorylation (Aerobic)
Now we are around the 80-second mark of this intense hike, but you start to slow down dramatically because of a few factors: your muscles are burning, you have run out of PCr, and you have reached the maximum capacity for glycolysis. At this point, the energy system that helps you keep going is known as oxidative phosphorylation. This system has more oxygen available to it and yields the most ATP, and it can do so for a very long time (it is the central energy system during endurance sports). This process uses two systems inside the mitochondria (energy factories inside cells) to generate ATP: the Krebs cycle (a process that generates most of the ATP during